The Pentagon has released a public defense of its decision to fulfill a massive cloud-migration initiative with a single cloud provider, pushing back on several tech industry powerhouses that argue the looming multi-billion-dollar contract should be divided among vendors.

Officials at the Department of Defense believe it will best serve troops in the field to place data in the hands of one Infrastructure-as-a-Service provider, said the letter sent last week to congressional committees.

The letter was originally intended not to be disclosed to the public, but the Pentagon opted for more transparency amid protests from news outlets and congressional staffers. The single-cloud posture flies in the face of advice from an IT trade consortium that urged a multi-cloud approach.

The ITI letter argued a multi-cloud approach would adhere to best practices for ensuring price competitiveness and avoiding vendor lock-in.

Bloomberg News got hold of spending figures that indicate the government plans to spend $1.63 billion on cloud services over the next five years, starting with $160 million next fiscal year.

The Pentagon said it wants submittals to include plans to avoid vendor lock-in so that within two years it can consider switching to another provider. Leveraging application containers is one way, the military believes, it can migrate if it decides not to commit to three- and five-year extensions stipulated in the contract.

The military's IT leaders are concerned that multiple providers will increase security management challenges and make data less accessible to U.S. forces deployed in remote settings, such as naval vessels, the report said.

Oracle has already successfully scuttled the lion's share of a U.S. TRANSCOM contract to AWS partner REAN Cloud that many viewed as a precursor to the larger contract for which it will solicit bids later this year.